Build Firefox Faster with Build Splendid

August 15, 2012 at 02:30 PM | categories: Mozilla, Firefox, build system

Would you like to build Firefox faster? If so, do the following:

hg qimport
hg qpush
rm .mozconfig* (you may want to create a backup first)
./mach build

This should just work on OS X, Linux, and other Unix-style systems. Windows support is currently broken, sorry.

mach can do much more than build. Run the following to see what:

./mach --help

Important Info

mach replaces mach has its own configuration file. The first time you run mach, it will create the file mach.ini in the same directory as the mach script. This is your new mozconfig file.

The default mach.ini places the object directory into the directory objdir under the top source directory. It also builds an optimized binary without debug info.

Run the following to see which config settings you can add to mach.ini:

./mach settings-create
./mach settings-list

This may fail because I'm still working out the kinks with gettext. If it doesn't work, open python/mozbuild-bs/mozbuild/ and search for _register_settings. Open python/mozbuild-bs/mozbuild/locale/en-US/LC_MESSAGES/mozbuild.po for the help messages.

As a point of reference, my mach.ini looks like the following:

application = browser

configure_extra = --enable-dtrace --enable-tests

cc = /usr/local/llvm/bin/clang
cxx = /usr/local/llvm/bin/clang++

cflags = -fcolor-diagnostics
cxxflags = -fcolor-diagnostics

source_directory = /Users/gps/src/mozilla-central-git
object_directory = /Users/gps/src/mozilla-central-git/objdir

I am on OS X and am using a locally-built version of LLVM/Clang, which I have installed to /usr/local/llvm.

You'll notice there are no options to configure make. The patch automatically selects optimal settings for your platform!

Known Issues and Caveats

This is alpha. It works in scenarios in which I have tested it, mainly building the browser application on OS X and Linux. There are many features missing and likely many bugs.

I have been using this as part of my day-to-day development for weeks. However, your mileage may vary.

As stated above, Windows support is lacking. It will appear to work, but things will blow up during building. Don't even try to use it on Windows.

There are likely many bugs. Please don't file Bugzilla bugs, as this isn't part of the build system just yet.

This patch takes over the build system. Do not attempt to use or run make directly with this patch applied.

If you encounter an issue, your methods of recourse are:

  1. Post a comment on this blog post
  2. Ping me on My nick is gps. Try the #buildfaster channel.
  3. Send an email to

I am particularly interested in exceptions and build failures.

If you encounter an issue building with this, just reverse the patch and build like you have always done (don't forget to restore your mozconfig file).

If mach.ini does not support everything you were doing in your mozconfig, please send me a copy of your mozconfig so I can implement whatever you need.

Other Info

I will likely write a follow-up post detailing what's going on. If you are curious, the code lives in python/mozbuild-bs. The backend and frontend sub-packages are where the magic is at. Once the backend has been configured, check out and all of the files in the object directory.

I am particularly interested in the real-world impact of this patch on people's build times. In this early version of the patch, you likely won't see drastic speed increases. On my MacBook Pro with an SSD, I see end-to-end clobber build times decrease by over a minute. With a little more work, I should be able to shave another minute or two off of that.

I will try to keep the patch up-to-date as I improve the build system. Refresh early and often.